P2 Steam Turbine Evolution

Steam Turbine Evolution
Gulshan Sachdev
Founder Director
SYNERGEM
www.synergemindia.com

Pinnacle of Steam Engine
The labors of generations of engineers had raised steam
engine to a very high degree of excellence
By late 1800's steam reciprocating engine had reached its
pinnacle and practically reached the limit of its
developmentdevelopment
To get more horse power the engine had to be bigger and
the size of the moving components was imparting vibration
to the engine, causing it to breakdown
No further refinement of design was capable of affecting
any substantial increase in its efficiency

Need of Steam Turbine
• Evolution of electricity generation started during the 1820s
and early 1830s by the British scientist Michael Faraday
• Reciprocating steam engines were used as prime movers to
generate electricity
• But steam engines were been so loud and noisy that
complaints about the noise of one in Manchester had forcedcomplaints about the noise of one in Manchester had forced
the power station to close.
• The need for a rotating machine to convert the power of
steam directly into electricity was realized and developments
were started
• The problem with Turbine was one of basic engineering: the
reciprocating engine utilizes the pressure of steam, but the
turbine principle uses the speed of steam

Challenges of Steam Turbine
It was evident that a jet of steam could be made to turn a
wheel by acting on blades set around its circumference -
Impulse
Alternatively it could be used to develop power by itsAlternatively it could be used to develop power by its
own reaction when escaping tangentially from an orifice
in a rotating wheel or arm - Reaction
Both devices had already been suggested by innumerable
inventors, but the difficulty lay in controlling the velocity
of the steam

Even steam at a comparatively low pressure escaping into the
atmosphere may easily be travelling at more than 2500 feet
per second, or over I700 miles an hour, while twice this
velocity may be attained by high-pressure steam flowing into
a good vacuum.
To make use of such velocities effectively in a simple turbine,To make use of such velocities effectively in a simple turbine,
the blades or other moving elements would have to travel at
about half the speed of the steam, for otherwise an undue
proportion of the energy of the jet would be uselessly carried
away in the steam leaving the wheel.
The blade speeds required for efficiency would therefore be
so high that they would be prohibited by reason of centrifugal
force alone, apart from other considerations

Even by the 1880's it was just not possible to construct a
device that could rotate at 1000 mph without melting or flying
apart, probably both
Watt disposed competition of steam turbine with steam
engines with remark that 'Without God makes it possible for
things to move 1000 feet per second, it cannot do much harm'

Sir Charles Parson and Development of
Steam Turbine
The modern steam turbine and turbo generator both owe a lot to a
great mechanical engineer Sir Charles Parsons
No man has made a greater contribution to human welfare than Sir
Charles Parsons by the revolutionary improvements he broughtCharles Parsons by the revolutionary improvements he brought
about in the use of steam
Sir Charles Parsons possessed the genius and courage to foresee
the wide diversity of the duties to which the turbine could be
applied
Problem after problem was solved in the most admirable way

Sir Charles Parsons Steam Turbine
Charles Parsons, realized the need for a rotating machine
(turbine) to convert the power of steam directly into
electricity
It was in 1884 that Parsons developed and patented the firstIt was in 1884 that Parsons developed and patented the first
workable turbine engine and electrical generator
Within five years 350 of Parsons’s steam turbines were
supplied.

Controlling the speed of Turbine
His genius looks simple in retrospect, like all great ideas
Since he could not create a device that could rotate at the
speed of steam, he slowed the steam down
It was known that the speed of a jet of steam will obviously
depend upon the difference of pressure that causes the flow
A vacuum, or partial vacuum, at the exhaust end of the engine
would create a higher pressure ratio between input and
output, hence higher velocity steam jet

It occurred to Parsons that he could attain this by causing the
whole expansion of the steam to take place in a series of steps
This effectively resulted in a smaller pressure drop between feed
and exhaust and a slower steam jet.
Each partial drop of pressure being only sufficient to generate a
velocity that could be efficiently utilized by blades running at a
moderate speed.
By repeating this process a number of times most of the energy
from the steam jet can be extracted without the turbine having
to destroy itself. www.synergemindia.com

To put this idea into effect he constructed a turbine
consisting of a cylindrical rotor enclosed in a casing
The steam flowed along the annulus between the two,
parallel to the axis of the machine, and in so doing it had toparallel to the axis of the machine, and in so doing it had to
pass through rings of blades fixed alternately in the casing
and rotor
The passages between the blades of each ring formed
virtually a set of nozzles in which a partial expansion of the
steam could take place

In passing through each ring of fixed blades the steam
acquired a certain velocity due to this expansion, and the
jets so formed gave up their energy in driving the
succeeding row of moving blades.succeeding row of moving blades.
The passages between the moving blades also acted as
nozzles, permitting a further partial expansion, so that the
moving blades were impelled partly by the 'action' of the
steam entering them and partly by the 'reaction' of the
steam leaving them.

A simple turbine schematic of the Parsons type
Steam pressure drops by a fraction of the total across each
pair of rotating and fixed blades, the stators grow larger as
pressure drops

The principle of subdividing the whole expansion of the steam into a
number of stages, so that only comparatively moderate velocities
have to be dealt with, still forms the basis of all efficient turbine
design
The secondary principle of utilizing the 'reaction' of the steam
expanding in moving blades has remained typical of the Parsonsexpanding in moving blades has remained typical of the Parsons
turbine
It is not, however, a crucial characteristic of an efficient turbine, and
certain inventors subsequent to Parsons, notably C. G. Curtis in the
United States and Professor A. Rateau in France, preferred for
constructional reasons to confine the expansion of the steam to
fixed nozzles.

Machines of the latter type, in which the steam drives the
blading of each stage by virtue of its velocity, only, are known
as 'impulse' turbines
Although they have attained an honorable position in the
industry, it is generally recognized that the 'reaction' principle,
chosen by Parsons for his original turbine, is conducive to the
highest efficiency, so that large machines which are nominally
of the impulse type are now often designed to work with a
certain amount of reaction in their blading

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P2 Steam Turbine Evolution

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